The invention relates to a separating device, consisting of support plates and cut sections of a semi-permeable diaphragm, for fluids flowing on both sides of the diaphragm in separate flow paths. The separate flow of the fluids is assured by stringlike or bandlike sealing elements held in the support plates.
In a known separating device disclosed in German (DE-GM 70 22 655), support plates of plastic material are used which are covered by cut diaphragm sections over their whole surface. In the area of the outer border, thin sealing ribs are provided on the support plate, for the separation of the various flow paths and for the total sealing of the flow chambers. The sealing ribs are pressed by the contact pressure into the microporous diaphragm structure. The diaphragm performs sealing function in the area of the sealing rib.
This kind of sealing is unsatisfactory, because of manufacturing tolerances, no plane parallel shaping of the plates and the sealing ribs is possible and the diaphragm must have a certain strength in order to function as a seal.
Depending on the purpose, such as for dialysis, for ultrafiltration, for reverse osmosis, and on the type of the fluids to be treated, be it liquids or gases, special diaphragms must be selected to make an optimum material separation possible. It is therefore known to include, in addition to the support plates, also special sealing plates for better sealing between the individual layers of the support plates as disclosed in U.S. Pat. No. 3,831,763. The sealing frames are flat cut sections of a special sealing material. The special sealing material must--like the diaphragm and the plastic material plates--be capable of being autoclaved repeatedly, therefore no sealing material is suitable for all purposes of the separating device. The support plates of plastic material must have a certain strength so that they are not distorted in the autoclaving and can resist the clamping forces of the total device. The additionally necessary sealing frames raise the cost of the total structure of such a package-like separating device and present additional danger points for the occurrence of leakage.
A more recent concept as disclosed in German (DE-OS 29 30 986) consists in sealing by means of sealing ribs molded into the support plates. Such a sealing becomes problematical in the area of the inlets and outlets which are in most cases shaped as circular bores which penetrate the entire stack of the support plates and are horizontally converted into secondary-distribution channels.
U.S. Pat. No. 3,585,131 discloses a structure in which the support plates slot perforations pass over the entire width of the diaphragm over which the fluid flows, in order to achieve a better distribution of the fluid flows. In this known separating device the diaphragm consists of interwoven hollow fiber diaphragms through which the flow passes crosswise and over which it passes vertically. The fabric-like diaphragm is sealed, for the purpose of separating the three fluid spaces against the support plates, by a plastic material pasting layer. This construction and the sealing is very expensive to manufacture. The fabric-like structure also results in the danger that the sealing material does not satisfactorily penetrate the interspaces of the fabric and envelop the individual hollow fiber diaphragms and seal them off against the support plates.
In deviation from the use of support plates rigid in themselves, it is already known to form separating elements in multilayers from a plastic fabric with a fleece-like support material arranged on both sides, and from the diaphragms arranged on both sides. The sealing of the individual separating units is accomplished by spraying a synthetic resin around the entire outer border of the separating element. The fluid flows are distributed within the separating element through spaced bores arranged at the borders, for the mutual separation of the fluid paths. The adjacent bores are connected alternately on the outside and inside by an arched seal of synthetic resin over the sealed-off outer borders as disclosed in DE-OS 29 20 253 and U.S. Ser. No. 906,922.
This type of seal is also unreliable since it depends essentially on the control and exact limitation of the depth of penetration of the synthetic resin into the individual layers of the separating element.
Reference is also made to U.S. Pat. Nos. 4,113,625, and 3,497,423 which disclose various geometrical forms of the separating elements, sealing elements and support plates.